1. Field of the Invention
The present invention generally relates to automotive-type air conditioning refrigerant fluid dryer systems. More specifically, this invention relates to an air conditioning receiver/dryer assembly composed of a receiver tank and desiccant cup assembly that are configured to enhance the operation and durability of the receiver/dryer assembly and facilitate its assembly.
2. Description of the Prior Art
Automotive air conditioning systems use a compressor which compresses a vaporized refrigerant fluid, such as freon or an alternative refrigerant, to raise the temperature of the refrigerant fluid, which is then cooled and returned to a liquid state with a condenser. As a result, heat added to the refrigerant fluid in the compressor is transferred out of the system. The cooled refrigerant fluid is then sprayed through a thermal expansion valve into an evaporator where it is again vaporized. The heat of vaporization required for vaporizing the refrigerant is drawn from incoming outside air flowing or blown through the evaporator. Excess humidity contained within the incoming air is removed as condensation on the evaporator, therefore also drying the incoming air. The cooled, dry air then enters the passenger compartment of the vehicle, while the refrigerant is drawn back to the compressor where it is again compressed and the cycle repeated.
In automotive-type air conditioning systems, a receiver dryer device is typically employed between the condenser and the thermal expansion valve. Receiver/dryers remove any remaining moisture from the circulating refrigerant fluid with the use of a desiccant contained within the receiver/dryer, so as to ensure that the refrigerant fluid delivered to the expansion valve is in a liquid phase and free of condensation. Various forms of receiver/dryer devices have been suggested in the prior art. Generally, such devices include a cylindrical container having an inlet and an outlet for connecting to the refrigerant circuit. The desiccant is typically contained in a pack or otherwise restrained within the cylindrical container. The construction of the receiver/dryer device is such that refrigerant flow is directed through the desiccant, so that the desiccant can perform its intended function of removing moisture from the refrigerant. A tube is often used to return the refrigerant from one end of the container, into which the refrigerant is discharged after having passed through the desiccant, to the opposite end of the container, which is typically the same end through which the refrigerant originally entered the container.
It is generally conventional in the art to form the cylindrical container from a metal such as aluminum or an aluminum alloy, necessitating that separate subcomponents of the container be joined by brazing, welding, crimping or other suitable mechanical methods. Brazing, such as the tube-to-container braze joint seen in U.S. Pat. No. 3,545,227 to Grahl, can be problematic in that there may be braze residue remaining in the joined regions which may lead to contamination or pinhole leaks within the assembly. If the resulting leak is to the environment, a loss in the pressurized refrigerant fluid charge will result, while internal leaks can cause icing to occur within the air conditioning system or cause the system to operate as if it were undercharged. As an alternative to brazing for aluminum or steel materials, arc welding may be used to join the various components. However, the arc welding process can also be problematic in that it may result in detrimental dimensional changes to the assembly. Finally, various mechanical joining methods, such as a press fit between the tube and container, as taught by U.S. Pat. No. 5,038,582 to Takamatsu, can result in inadequate seals due to tooling variances and dimensional tolerances.
Similarly, numerous methods and components have been suggested for containing the desiccant. For example, U.S. Pat. Nos. 3,064,819 to Jones, 4,177,145 to Schumacher, 4,209,401 to Henton, 4,266,408 to Krause, 4,354,362 to Schumacher et al., 4,811,571 to Mayer and 5,364,540 to Sciuto teach the use of a biasing member of one sort or another in conjunction with a pad, screen or filter for the purpose of compacting the desiccant, so as to reduce the amount of relevant movement between the individual desiccant particles. Such a capability is generally an important aspect of receiver/dryer designs, since relative movement of desiccant particles will tend to cause damage to the particles through abrasion, ultimately reducing the effectiveness of the desiccant and adding particles to the refrigerant fluid which may damage the air conditioning system.
While spring-biased securement of the desiccant generally serves its purpose well, it would be preferable to avoid the additional cost and assembly steps required to position and secure a spring within the container. The prior art has suggested alternative methods for containing a desiccant, such as appropriately sizing a cartridge in which the desiccant is contained, as taught by U.S. Pat. No. 4,436,623 to Cullen et al. However, such cartridges are filled with desiccant based on weight, such that the amount of desiccant deposited in a pre-sized cartridge can vary as a result of variations in desiccant density. Consequently, an underfill condition can result that permits excessive agitation of the desiccant particles. This results in the desiccant abrading and breaking down into smaller particles which may leak into the system. Another alternative is to form a molded desiccant core, as taught by U.S. Pat. No. 4,320,000 to Lange et al. However, such an approach adds unwanted processing cost to the desiccant material.
From the above discussion, it can be readily appreciated that, while receiver/dryer devices are a desirable component within automobile air conditioning systems, the manufacturing processes used to form such assemblies are often complicated by the various joining operations required and the additional components required to properly restrain the movement of the desiccant material. Accordingly, what is needed is an improved receiver/dryer device that avoids the shortcomings of the prior art. In particular it would be desirable to provide a receiver/dryer assembly that is manufactured from a minimal number of components, so as to reduce the number of joining operations required and thereby the potential for leaks. Further, it would also be particularly desirable if such a receiver/dryer assembly were configured to readily adapt to variations in fill level of the desiccant without requiring additional biasing devices and additional desiccant processing, be configured to prevent blowby of the refrigerant fluid, and be keyed to prevent improper assembly of the device.